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Choosing a Motor Oil for a GDI or T/GDI Engine

 

Man in a store comparing the labels on different motor oils on a display shelf with one he is holding

GDI (Gasoline Direct Injection)and T/GDI (Turbocharged Gasoline Direct Injection) engines use a fuel delivery system that bypasses the intake valves and injects the gasoline directly into the cylinders.

Although it has many advantages in terms of power and fuel economy, GDI fuel delivery also dramatically increases the potential for carbon buildup on the intake valves, which I discuss in more detail on this page.

The nutshell version is that because the gasoline in a GDI or T/GDI engine never touches the seating area of the intake valves, the gasoline can't keep the valves clean. We don't get the "fuel wash" effect that happens on carbureted and port-fuel injection engines, in which the gasoline itself helps remove deposits from the intake valves.

The other thing to understand is that part of the reason the intake valves develop deposits in the first place is because of vapors given off by the hot oil when the engine is running. Those vapors are routed to the engine's air intake by the PCV (Positive Crankcase Ventilation) valve to reduce engine emissions. That's why the oil's volatility — its tendency to produce vapors at operating temperature — is such a critical consideration when choosing oil for a GDI engine. The lower the oil's volatility, the less it will contribute to intake valve deposits.

 

What to Consider When Choosing an Engine Oil

1. Manufacturer Requirements

The first place to look when deciding which oil to buy choose for a GDI engine (or any engine, for that matter) is the owner's manual. Make sure that you use an oil that meets the manufacturer's specification. This usually will include a viscosity range and an industry standard, such as an API standard in North America or an ACEA standard in Europe.

Some auto manufacturers also have their own standards for motor oils, such as GM's Dexos® standards or Ford's WSS standards. A few manufacturers even require that specific, manufacturer-approved oils be used. To preserve your vehicle's warranty, you must limit your oil choices to those that meet or exceed your vehicle's manufacturer's specifications.

That being said, there's a big difference between oils that barely meet a standard and those that exceed it. In all cases, but especially if your car has a GDI engine, choosing an oil that's better than just "good enough" can help extend your engine's life and reduce maintenance costs.

2. The Oil's Volatility

Because the crankcase oil vapors fed back into the intake system by the PCV system are a major cause of carbon fouling of the valves, choosing an oil that is less volatile (one that offgasses fewer vapors) can reduce the carbon buildup at its source. The fewer vapors the oil gives off, the better. This is where Noack and TEOST numbers come into play. If you're interested, I talk more about Noack and TEOST as they relate to GDI and T/GDI engines here.

The condensed version is that the Noack test (also known as ASTM D-5800) is a measure of how much of an oil is lost to vapor at operating temperatures. The TEOST test (which has two versions known as ASTM D-6335 and ASTM D-7097) is a more direct measure of an oil's tendency to form deposits. All else being equal, you should look for oils with lower numbers for both Noack and TEOST when choosing motor oil for a GDI or T/GDI engine.

My personal standards when choosing an oil for my own GDI-engine car are a Noack score of 9 percent maximum, but preferably 6 percent or lower; and a TEOST of 15mg maximum, but preferably 8mg or less. Realistically speaking, volatility levels that low can only be achieved using synthetic oils, so that excludes conventional oils from my consideration for GDI or T/GDI engines.

You won't find Noack and TEOST numbers anywhere on the oil's label, but they usually can be found on spec sheets and marketing materials available from the manufacturers on their Web sites. If a company refuses to publish these numbers, then I recommend looking for another motor oil.

3. Whether the Oil Meets API, ACEA, and ILSAC Standards for Your Car

If you live in North America, one simple way to narrow down your choices is to look for an oil that meets the North American API standard specified by your car's manufacturer, the international ILSAC (International Lubricants Standardization and Approval Committee) GF standard, and the European ACEA (European Automobile Manufacturers Association) standards, for the same car and engine sold elsewhere in the world.

For cars sold in North America, manufacturers will usually specify an API standard for oil because API is the standard used in North America. The International ILSAC and European ACEA standards, however, tend to be more stringent and specific than the API standards. Limiting your motor oil choices to oils that meet the manufacturer's ACEA and ILSAC standard for your car, in addition to the API standard specified for your car in North America, will help narrow the field to only the very best motor oils for your car's engine.

For example, at the time of this revision, most late-model vehicle engines specified API Service Category SN or SN Plus oil (which has since been superseded by API Service Category SP) for GDI vehicles sold in North America, the ACEA A3/B3 or A5/B5 standards for the same cars sold in Europe, or the ILSAC GF-6A standards for the same cars sold elsewhere in the world. Choosing an oil that meets the newer API SP standard, the ACEA A3/B3 or A5/B5 standard, and the ILSAC GF-6 or GF-6A standard, rules out all but the very best oils by eliminating those that can't meet the most stringent requirements.

My Personal Favorite Oils for GDI and T/GDI Engines

If all you want to do is choose a decent oil for your car's GDI or T/GDI engine, with as little fuss as possible, just limit your oil choices to any top-shelf oil made by a major manufacturer that meets your car manufacturer's requirements and is marketed for GDI and T/GDI engines. You won't find any bad oils among the top-shelf products made by major manufacturers like Pennzoil, Castrol, Royal Purple, Mobil, Total, and Valvoline. These companies have too much to lose to put out bad oils, especially when it comes to their flagship products.

At the time of this revision, my favorite motor oils for GDI and T/GDI engines are Castrol Edge Titanium, Pennzoil Ultra Platinum, Mobil 1, Total Quartz INEO, and Valvoline Modern Engine Oil. They all have very good Noack and TEOST scores and excellent overall lubricity. But do your own research. This is a period of very rapid advancements in engine oil technology. By the time you read this page, there may be even better oils out there.

One good place to do research (as well as engage in discussions and arguments with people who really take oil seriously) is at Bob is the Oil Guy, an online forum and Web site dedicated to oil and other closely-related automotive topics. If you're really, really into oil, I suggest you sign up. It's a great place to hang out with other oil geeks.

The oil I'm using right now is Castrol Edge Titanium Advanced. Although my car never had a serious oil-burning problem, after two oil changes with the Castrol product (each preceded by an induction system cleaning using CRC Intake Valve Cleaner or Berryman Intake Valve and Combustion System Cleaner), my car's oil consumption has dropped to zero. It's like the oil level is painted on the dipstick. It hasn't budged.